| Selective catalytic oxidation of NO is the key of the reduction of nitrogen oxides and sulfur dioxides simultaneously in power plants. The paper focused on the research of the catalyst, which was the main difficulty in the SCO technology. Cr oxides were used as the active site and Ce oxides were used as the promoter in the system of the NO oxidation. TiO2-PILC was chosen as the support of Cr-Ce based catalysts, which was one of the promising supports in the catalysis. The paper aimed to synthesize the CrCe/TiO2-PILC nanocomposites, figure out the interaction between the Cr, Ce and TiO2-PILC and analysis the catalystic activity.The first part of our research was to compare the activities between Cr/TiO2-PILC and Cr/TiO2serving as the oxidation catalyst. Both of the two catalysts showed the best activity when they were doped10%weight chromium. Comparing each spot, the Cr/TiO2-PILC had better activity than Cr/TiO2. To analyze the reason of the difference, the BET,、XRD、SEM、 TPR and XPS were used in the experiment. BET result indicated that the large surface area of TiO2-PILC could benefit the dispersion of active site. Cr6+existed on the surface of Cr/TiO2-PILC, which would enhance the oxidation ability. EPR and XPS analysis explained the concrete process of NO oxidation over Cr/TiO2-PILC. Cr3+was the center of the action and absorbed O2, which could transfer one electronic to form O2-. Cr6+absorbed NO. When NO+O2were adsorbed simultaneously, the intensity evolution of superoxide ions increased. The existence of O2-reacted with the intermediate NO*and then turned into NO3-.The second part was about the promotion effect of Ce. A series of chromium-ceria doped on TiO2-pillared clay nanocomposites catalysts with various Cr/Ce ratios were investigated in the oxidation of NO. The activity order decreased as below:Cr(1)Ce(0.25)TiP Cr(1)Ce(0.5)TiP> Cr(1)Ce(0.17)TiP>Cr(1)Ce(0)TiP>Cr(1)Ce(1)TiP. The Cr(1)Ce(0.25)TiP calined under500℃showed best oxidation activity. Cr(l)Ce(0.25)TiP nanoparticles were round-shaped and the average particle size was less than10nm. The particles were well dispersed. The ease of formation of labile oxygen vacancies and particularly the relatively high mobility of bulk oxygen species of CeOx could increase the concentration of chemisorbed oxygen. Therefore. the certain amount of CeOx was beneficial to the oxidation reactions. The transition from Ce4+to Ce3+could create a charge imbalance, the vacancies and unsaturated chemical bonds on the catalyst surface and thus facilitated the formation of chemisorbed oxygen. The binding energy of Ti shifted to the higher field with the content of CeOx increasing, which indicated that the electron density around Ti atoms decreased. It resulted from the powerful electron withdrawing ability of Ce. The shift proved the incorporated reaction between Ce and the Ti as well.The third part of the paper researched about the technological condition of Cr(1)Ce(0.25)TiP. The low space velocity improved the residence time and enhanced the activity. When NO concentration increased, the conversion from NO to NO2decreased. The performance of sulfur and water resistance was studied as well. The result showed that the catalyst showed a good resistance to SO2and H2O. When SO2and H2O were added in the feed gas, the catalytic activity decreased but when removed, the activity recovered. The deactivation was not totally irreversible. |
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